1. Field of the Invention
The present invention relates to a fine-fibers-dispersed nonwoven fabric, a process and an apparatus for manufacturing the same, as well as a sheet material comprising the same.
2. Description of the Related Art
Many functions can be imparted to a nonwoven fabric by appropriately combining a selection of fibers used, processes for manufacturing a fiber web, and/or processes for bonding a fiber web, and therefore, the nonwoven fabric has wide applications. For example, a nonwoven fabric composed of fine fibers having a fiber diameter of 4 μm or less and a fiber length of 3 mm or less has excellent filtering characteristics, and thus, can be preferably used as a gas or liquid filter. Further, the nonwoven fabric has a good pliability, and thus, can be preferably used as an interlining cloth.
One of the conventional processes for manufacturing such a nonwoven fabric composed of fine fibers having a fiber diameter of 4 μm or less and a fiber length of 3 mm or less comprises the steps of forming a fiber web from islands-in-sea type composite fibers, namely, fibers prepared by dispersing resin components (islands components), difficult to be removed by a particular solvent, into a resin component (sea component) capable of being removed by the particular solvent, in accordance with a carding method or an air-laid method, entangling fibers by an action of needles or a water jet to form an entangled fiber web, and then,
removing therefrom the sea components of the islands-in-sea type composite fibers by the solvent to generate the fine fibers of the island components. This process can provide a nonwoven fabric composed of fine fibers having a fiber diameter of 4 μm or less and a fiber length of 3 mm or less. Nevertheless, the fine fibers are present as bundles in the nonwoven fabric, and thus, the nonwoven fabric is not too different from a fabric composed of thick fibers, and therefore, the filtering characteristics or pliability are not sufficient.
There is a known process for manufacturing a nonwoven fabric, which process can remedy the bundles of the fine fibers. The process comprises the steps of taking up fine fibers having a fiber diameter of 4 μm or less and a fiber length of 3 mm or less from a slurry containing dispersed fine fibers, to form a fiber web, and then bonding the fiber web. This process can provide a nonwoven fabric composed of the dispersed fine fibers. Nevertheless, the fiber web formed by taking up the fine fibers from slurry has a high apparent density, because the fine fibers therein are closely bonded with each other. Therefore, when the nonwoven fabric is used as a filter, a pressure loss becomes high.